1. Field of the Invention
This invention relates to integrated circuit processing and, more particularly, to a process for depositing a non-conductive barrier layer such as a nitride film onto a copper surface.
2. Description of the Related Art
A high density integrated circuit typically comprises numerous electrical devices and conductors formed on multiple layers of conducting and semiconducting material that are deposited and patterned in sequence onto a substrate surface. Additionally, insulating material is typically positioned between the individual devices so as to electrically isolated the devices from one another. In particular, intermediate insulating layers, better known as interlevel dielectrics (ILDs), are typically interposed between conducting layers in a circuit so as to electrically isolate components formed on adjacent layers. The insulating layers inhibit electrical shorts and preserve device integrity.
An integrated circuit is operable when its individual components are interconnected with an external source and with one another. In particular, designs of more complex circuits often involve electrical interconnections between components on different layers of the circuit as well as between devices formed on the same layer. Such electrical interconnections between components are typically established through electrical contacts formed on the individual components. The contacts provide an exposed conductive surfaces on each device where electrical connections can be made. However, in a multilayer, high density integrated circuit, the components are often buried in internal sublayers of the circuit where insulating material are deposited over the components making the establishment of electrical contacts difficult.
One method of creating electrical contacts on devices located in the sublayers of the circuit is by forming openings in the interlevel dielectrics (ILDS) that are deposited over the components. The openings, known as contact vias or holes, typically extend downwardly from a top surface of the ILD to the layer containing the electrical devices so that a top surface of the device is exposed. Furthermore, the openings are then filled with a conductive material, such as copper, which effectively establishes electrical contact for components located underneath the ILD.
In addition to contact vias, trenches can also be etched onto the surface of the insulating material in a desired pattern for a conductor layer in a process that is commonly known as the damascene process. In a typical damascene process, the trenches are etched on the surface of the insulating material comprising an ILD and subsequently metalized so as to produce integrated conductors. In particular, the trenches are metalized in a similar manner as that of the contact vias wherein the trenches are filled with a conductive material so as to establish a desired conductive path.
The metalization process generally involves depositing a layer of conductive material such as copper into the vias or trenches, thereby interconnecting electrical devices and wiring at various levels. In a multilayer integrated circuit assembly, an insulating layer is typically deposited onto the metalized vias or trenches so as to electrically isolated the metalized vias or trenches from additional circuit layers that will be formed in a stacked configuration above the vias or trenches. In particular, the insulating layer typically comprises an oxide material such as silicon dioxide wherein the oxide electrically isolates devices formed on adjacent circuit layers. Disadvantageously, however, the oxide layer will lose its insulating properties when copper or other conductive material diffuses from the underlying adjacent layer into the oxide layer. In particular, metal that migrates into an insulating oxide layer can effectively short out the devices electrically isolated by the layer.
To address this problem, a non-conductive barrier layer is generally interposed between the conductive layer and the adjacent insulating layer wherein the barrier layer inhibits metal from diffusing into the insulating layer. In particular, a non-conductive barrier layer typically comprises a nitride film and is preferably positioned between a top surface of a copper wiring layer and a bottom surface of an adjacent oxide layer so as to inhibit copper from migrating upwardly into the oxide layer. Furthermore, the nitride film can be deposited onto the copper surface by using well known deposition techniques such as evaporation, sputtering, chemical vapor deposition, or plasma enhanced chemical vapor deposition (PECVD).
However, one disadvantage of the standard nitride PECVD process is that the nitride film is known to react with a top surface of the copper layer during the deposition process and will consequently alter the electrical properties of the copper. In particular, the copper and nitride reaction is shown to substantially increase the copper line resistance, which in turn will delay signal transmission between devices. Slow signal transmission is not favored in most semiconductor devices, particularly in high speed, high density integrated circuits. Furthermore, high speed integrated circuits generally require conductors with low electrical resistance so as to facilitate current flow and signal transmission. Therefore, a reduction in copper line resistance is not only desirable but necessary in light of the constant demand for integrated circuits with higher speed and increased device density.
Hence, from the foregoing, it will be appreciated that there is a need for a process of depositing a non-conductive barrier layer so that any increase in the electrical resistance of the underlying conductive wiring or contact is reduced. To this end, there is a particular need for a process of depositing a non-conductive barrier layer wherein the barrier layer will not unfavorably increase the copper line resistance.
The aforementioned needs are satisfied by the method of forming a conductive interconnect integrated circuit of the present invention. In one aspect, the present invention comprises a method of depositing a layer of non-conductive barrier film onto a layer of conductive material wherein the deposition process does not affect the electrical resistance of the metal, so that the resistance of the conductive material remains substantially the same before and after the deposition of the non-conductive barrier layer.
In one embodiment, the method comprises depositing a silicon nitride non-conductive barrier layer onto a copper surface is provided wherein the method includes a low temperature plasma enhanced chemical vapor deposition process (PECVD) wherein the PECVD process temperature range is held between 150 C.-300 C. In particular, the low temperature range as disclosed in the present invention is shown to inhibit a reaction between the silicon nitride and copper that typically occurs during the standard high temperature (400xc2x0 C.) silicon nitride PECVD process. Such reaction between the silicon nitride and copper is generally not favored as it results in the formation of silicide in the copper, which in turn will unfavorably increase the line resistance of the copper.
Furthermore, the undesired silicide formation in copper is also known to occur in a reaction between the silane gas used as part of the PECVD process and the exposed copper surface when the PECVD process is conducted in a high temperature environment as taught by prior art. In contrast, the process parameter as disclosed by the preferred embodiment is shown to inhibit this particular reaction between the silane gas and copper so as to further inhibit the formation of silicide in copper. Alternatively, a layer of amorphous silicon carbide is also shown to be an effective non-conductive barrier layer that does not unfavorably increase the resistance of the copper. Preferably, the amorphous silicon carbide is deposited onto the copper surface using a similar PECVD process with a process temperature of approximately 400 C.
From the foregoing, it will be appreciated that the aspects of the present invention provide a method of depositing a non-conductive barrier layer onto a metal surface without increasing the resistance of the metal. In particular, the method provides a novel low temperature plasma enhanced chemical vapor deposition (PECVD) process wherein the low temperature processing environment is shown to inhibit the formation of silicide in the copper, thereby avoiding the undesired increase in copper line resistance that will otherwise result from using known PECVD process parameters. These and other objects and advantages of the present invention will become more apparent from the following description taken in conjunction with the following drawings.